title: Inhibition by SKF 525-A of 7-ethoxycoumarin O-deethylation in microsomal and the reconstituted monooxygenase systems from PCB-treated rat livers.
abstract: Addition of diethylaminoethyl 2,2-diphenylvalerate-HCl (SKF 525-A) to the incubation mixture containing liver microsomes or purified cytochrome P-450 (PCB P-450) from PCB (KC-500)-treated rats resulted in non-competitive inhibition of 7-ethoxycoumarin O-deethylation activity whereas the addition to the incubation mixture containing purified cytochrome P-448 (PCB P-448) showed a competitive inhibition. Fortification of PCB-induced microsomes with purified NADPH-cytochrome P-450 reductase enhanced the O-deethylation activity. With the reductase-fortified microsomes, SKF 525-A inhibited the O-deethylation in a competitive manner. Based on these results, we confirmed that SKF 525-A inhibits non-competitively and competitively, depending on the species of cytochrome P-450. Our results also support the view that in microsomes from PCB-treated rats, PCB P-450 rather than PCB P-448 is mainly involved in the O-deethylation reaction, presumably due to the presence of a limited amount of NADPH-cytochrome P-450 reductase in microsomes.
mesh_terms: D015660:7-Alkoxycoumarin O-Dealkylase; D000818:Animals; D001667:Binding, Competitive; D019388:Cytochrome P-450 CYP1A2; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D003580:Cytochromes / Q000378:metabolism*; D066298:In Vitro Techniques; D008297:Male; D008862:Microsomes, Liver / Q000201:enzymology*; D009251:NADPH-Ferrihemoprotein Reductase / Q000494:pharmacology; D010105:Oxygenases / Q000037:antagonists & inhibitors*; D011078:Polychlorinated Biphenyls; D011335:Proadifen / Q000378:metabolism* / Q000494:pharmacology; D051381:Rats; D013379:Substrate Specificity
chemical_list: D003580:Cytochromes; D003577:Cytochrome P-450 Enzyme System; D011335:Proadifen; D011078:Polychlorinated Biphenyls; D010105:Oxygenases; D015660:7-Alkoxycoumarin O-Dealkylase; C017170:Cyp1a2 protein, rat; D019388:Cytochrome P-450 CYP1A2; D009251:NADPH-Ferrihemoprotein Reductase